1. Field of the Invention
This invention relates to polyphthalatecarbonate/polycarbonate resin blends and, more particularly, relates to polyphthalatecarbonate/polycarbonate resin blends exhibiting high level of resistance to yellowing and hazing from exposure to ultraviolet radiation.
2. Description of the Related Art
Aromatic polycarbonate resins, for example those derived from bisphenol A and phosgene, have found particular utility in glazing applications such as transparent sheets and films for windows. These polycarbonates, however, suffer from hazing and yellowing upon extended exposure to ultraviolet radiation. Prior solutions have involved the coating of these sheets and films and ultraviolet radiation absorbers. Coating technologies however suffer from a number of problems including the employ of expensive coatings and equipment and the use of organic solvents.
Polyestercarbonate resins also find widespread utility, particularly for glazing and transparent sheet applications demanding high impact resistance, high resistance to scratching, or high solvent resistance. However, the usefulness of polyestercarbonate resin is limited by its high susceptibility to, and rate of, yellowing during exposure to light, especially sunlight. For example during accelerated light aging studies, unstabilized polyestercarbonate resin becomes noticeably yellow (change in yellowness index of about 5) after less than 5 hours of exposure to RS sunlamps (see for example U.S. Pat. No. 4,556,606). This yellowing is the result of the polyestercarbonate resins, upon exposure to ultraviolet radiation, undergoing a photo-Fries rearrangement which converts ester bond linkages to ketone groups which results in a yellowing of the surface of the polyestercarbonate resin. Photo-Fries rearranging is discussed in Adv. Photochem, 8, 109-159 (1971) and in U.S. Pat. No. 4,534,104. Prior attempts to prevent this surface yellowing have involved applying ultraviolet radiation absorbing coatings to the polyestercarbonate resin articles but as set out above, coating technologies have a number of shortcomings.
An object of the present invention is to provide a thermoplastic resin which exhibits the excellent properties associated with aromatic polycarbonate resins and polyestercarbonate resins and which exhibits high levels of resistance to yellowing from ultraviolet radiation exposure.
Another object of the present invention is to provide a thermoplastic resin which is suitable for glazing applications and which exhibits high levels of resistance to ultraviolet radiation without the employ of ultraviolet radiation absorbing coatings.
An additional object to provide an aromatic polycarbonate resin blend which exhibits excellent resistance to yellowing upon extended exposure to ultraviolet radiation.